1. Field of the Invention
The invention relates to a negative-working radiation-sensitive mixture containing
a) a compound which generates a strong acid under the action of actinic radiation, PA1 b) a compound having at least two groups crosslinkable by acid and PA1 c) a polymeric binder which is insoluble in water and soluble or at least swellable in aqueous alkaline solutions. PA1 a) at least one compound which generates a strong acid under the action of actinic radiation, PA1 b) at least one compound having at least two groups crosslinkable by acid and PA1 c) at least one polymeric binder which is insoluble in water and soluble or at least swellable in aqueous alkaline solutions, PA1 R.sup.2 is hydrogen, chlorine, bromine or an alkyl, cycloalkyl, aryl or heteroaryl radical, or PA1 R.sup.1 and R.sup.2 together form a five- to eight-membered ring, PA1 R.sup.3 is hydrogen or an alkyl radical, PA1 R.sup.4 is hydrogen, halogen, nitro, acylamino, cyano, thiocyanato or an alkyl, alkenyl, alkynyl, aryl, aralkyl, alkylthio, arylthio or cycloalkylthio radical, PA1 R.sup.5 is hydrogen or an alkyl or aryl radical or PA1 R.sup.4 and R.sup.5 together form a five- to eight-membered ring, PA1 R.sup.6 is hydrogen halogen nitro, acylamino, cyano, thiocyanato or an alkyl, alkenyl, alkoxyalkyl, aryl, aralkyl, alkylthio, cycloalkylthio or arylthio radical, PA1 R.sup.7 is an alkyl or cycloalkyl radical, a perfluorinated or highly fluorinated alkyl radical or an aryl, arylalkyl or heteroaryl radical or an alkylene or arylene radical, PA1 m is 1 or 2, and PA1 n is 0, 1, 2 or 3. PA1 R.sup.10 to R.sup.14 are identical or different and are hydrogen, an alkyl, alkenyl, alkoxy, alkylthio or alkanesulfonyl radical each having up to 6 carbon atoms, a cycloalkyloxy, cycloalkylthio or cycloalkanesulfonyl radical each having up to 8 carbon atoms, a phenyl, styryl, phenoxy, phenylthio, benzenesulfonyl, phenylalkoxy, phenylalkylthio or phenylalkanesulfonyl radical which may be substituted on the aromatic ring and has up to 3 carbon atoms in the alkyl chain, hydroxyl, halogen, trifluoromethyl, nitro, cyano, alkoxycarbonyl, carbamoyl which may be substituted on the nitrogen by one or two alkyl radical(s) which may be linked to form a 5- to 7-membered ring, sulfamoyl which may be substituted on the nitrogen by one or two alkyl radical(s) which may be linked to form a 5- to 7-membered ring, alkanesulfonyloxy, arylsulfonyloxy, aylamino, alkylamino or arylamino, or two mutually adjacent substituents R.sup.10 to R.sup.14 form one or two further fused ring(s), and PA1 o is 0 or 1. PA1 R.sup.1 is a ferrocenyl radical, PA1 R.sup.2 is hydrogen, chlorine, bromine, alkyl, cycloalkyl or a radical of the formulae II or III or PA1 R.sup.1 and R.sup.2 together form a five- to eight-membered ring, PA1 R.sup.3 is hydrogen or an alkyl radical, PA1 R.sup.4 is hydrogen, halogen, nitro, acylamino, cyano, thiocyanato or an alkyl, aryl, alkylthio, arylthio or cycloalkylthio radical, PA1 R.sup.5 is hydrogen or an alkyl or aryl radical or PA1 R.sup.4 and R.sup.5 together form a five- to eight-membered ring, PA1 R.sup.6 is hydrogen, halogen, nitro, acylamino, cyano, thiocyanato or an alkyl, aryl, alkylthio, arylthio or cycloalkylthio radical, PA1 R.sup.7 is an alkyl or cycloalkyl radical, a perfluorinated or highly fluorinated alkyl radical or an aryl, arylalkyl, aryl or heteroaryl radical or an alkylene or arylene radical and PA1 m is 1 or 2 and PA1 n is 0, 1, 2 or 3. PA1 R.sup.2, R.sup.3, R.sup.4 and R.sup.6 are a hydrogen atom, PA1 R.sup.5 is a methyl group, PA1 R.sup.7 is a methyl, ethyl, trifluoromethyl, 1,1,2,3,3,3-hexafluoropropyl, phenyl, tolyl, 4-fluorophenyl, 4-chlorophenyl, 4-bromophenyl or 4-nitrophenyl radical, PA1 m is 1 and PA1 n is 0 or 1. PA1 A is -B- or -B-Y-B- and PA1 B is a substituted or unsubstituted mononuclear aromatic hydrocarbon or an oxygen- or sulfur-containing heterocyclic aromatic compound, PA1 Y is a single bond, (C.sub.1 -C.sub.4)alkylene or (C.sub.1 -C.sub.4)alkylenedioxy, whose chains can be interrupted by oxygen atoms, --O--, --S--, --SO.sub.2 --, --CO--, --CO.sub.2 --, --O--CO.sub.2 --, --CONH-- or --O--C.sub.6 H.sub.4 --O--, PA1 R.sup.4 and R.sup.5 are hydrogen, (C.sub.1 -C.sub.6)alkyl, C.sub.5 - or C.sub.6 -cycloalkyl, substituted or unsubstituted (C.sub.6 -C.sub.12)aryl, (C.sub.6 -C.sub.12)aralkyl or acyl, PA1 R.sup.6 is hydrogen, (C.sub.1 -C.sub.4)alkyl or substituted or unsubstituted phenyl, PA1 m is 0, 1, 2 or 3 and PA1 n is 1, 2, or 3, n+m being at least 2.
The invention also relates to a radiation-sensitive recording material produced with this mixture which is suitable for producing photoresists, electronic components, printing plates or for chemical milling.
2. Description of Related Art
To produce microelectronic circuits, several lithographic techniques are currently being used. Using g-line lithography (436 nm), which is usually applied to conventional diazonaphthoquinone/novolak formulations, resist images with a resolution of down to 0.8 .mu.m can be produced. Images of even finer structures (down to 0.5 .mu.m) on a resist layer can be obtained by means of i-line lithography (365 nm). More recent modifications of i-line lithography, such as, for example, phase-shifting mask technology, allow a further reduction in the size of the structures, of which images are to be formed, right down to about 0.35 .mu.m or less. An even higher resolution can be achieved with UV2 photoresists. In this case, two irradiation techniques are used: UV2 wide band exposure (240 to 260 nm) or exposure with KrF-excimer lasers which emit at 248 nm.
The continuing reduction in the size of the structures, for example in chip manufacture down into the range of less than 1 .mu.m, requires modified lithographic techniques. To form images of such fine structures, radiation of a short wavelength is used, such as high-energy UV light, electron beams and x-rays. The radiation-sensitive mixture must be adapted to the short wave radiation. A compilation of the requirements to be met by the radiation-sensitive mixture is given in the article by C. G. Willson "Organic Resist Materials--Theory and Chemistry" [Introduction to Microlithography, Theory, Materials, and Processing, editors L. F. Thompson, C. G. Willson, M. J. Bowden, ACS Symp. Ser., 219, 87 (1983), American Chemical Society, Washington].
There is therefore an increased demand for radiation-sensitive mixtures which can be used in the more recent technologies, such as mid-UV or deep-UV lithography [exposure, for example, with excimer lasers at wavelengths of 305 nm (Xef), 248 nm (KrF), 193 nm (ArF)], electron beam lithography or x-ray lithography, and which, furthermore, are preferably sensitive in a wide spectral region and correspondingly can also be used in conventional UV lithography.
Negative-working radiation-sensitive mixtures which contain bisazides as crosslinking agents and binders derived from isoprene are known. They are used as radiation-sensitive layers in the production of printing plates, printed circuits and integrated circuits. Their use in microlithography is, however, restricted by various technical disadvantages. Thus, it is difficult to produce qualitatively high-grade layers without pinholes. The heat holdout of such mixtures is inadequate, i.e., the resist images are distorted by thermal flow during processing. Finally, their resolution capacity is restricted to structures of &gt;2 .mu.m since, during the necessary development with organic solvents, they show undesirably high swelling even in the hardened areas, which in turn causes structure distortions or inhomogeneous developing processes and hence inadequate reproduction of the image predetermined by the exposure mask.
To be able to produce resist images having a resolution of better than 2 .mu.m, other negative-working radiation-sensitive mixtures have been developed which are sensitive to radiation of shorter wavelength, for example to high-energy UV radiation, electron beams or X-rays. Such a mixture contains, for example, a copolymer of 2,3-epoxypropyl methacrylate and 2,3-dichloropropyl methacrylate (DCOPA) or a combination of the corresponding homopolymers. The glass transition temperature of this mixture is, however, too low for many applications and, in particular, the low resistance of the mixture to plasma etching is undesirable. Furthermore, this resist material must be processed using developers based on organic solvents which are rather prone to pollute the environment. However, other hitherto known negative-working, aliphatically based photoresists also show a low resistance to plasma etching.
In EP-A 0,164,248, an acid-curable mixture was described which can be developed in aqueous alkaline media, has an improved plasma-etching resistance due to the use of aromatics and is sensitive to near UV light (350 to 450 nm). The acid generators mentioned here are especially sulfonic acid ester derivatives of diazonaphthoquinone, which form weakly acidic carboxylic acids on exposure and are therefore effective only in a comparatively high concentration. Due to the weak absorptions and the inadequate bleaching properties of the photolytic acid generator, however, such mixtures have a low sensitivity to DUV radiation, electron beams and x-rays.
In U.S. Pat. No. 3,692,560, an acid-curable mixture is described which contains an acid-crosslinkable melamine derivative, a novolak and chlorinated benzophenones as photolytic acid generators. These mixtures again do not have an adequate sensitivity in the deep UV region. Furthermore, hydrohalic acids are undesired as crosslinking catalysts, since these can, during the subsequent doping processes, undergo reactions with the dopants. Moreover, hydrohalic acids remaining in the cured resist have a strong corrosive action and can cause destruction of the material to be imaged and of the production equipment.
The same applies to the acid-generating derivatives of DDT, mentioned in EP 0,232,972, which are highly toxic and, if only for this reason, cannot be suitable for practice. Nevertheless, such compounds show a considerable sensitivity in the deep UV region (200 to 300 nm).
As the compounds which generate a strong acid on irradiation, especially onium salts, such as diazonium, phosphonium, sulfonium and iodonium salts of non-nucleophilic acids such as HSbF.sub.6, HAsF.sub.6 or HPF.sub.6 [see J. V. Crivello, Polym. Eng. Sci., 23 (1983) 953] have hitherto been used. In addition, halogen compounds, especially trichloromethyltriazine derivatives, trichloromethyloxadiazole derivatives, o-quinonediazidesulfonyl chlorides and o-quinonediazide-4-sulfonic acid esters have been recommended.
These compounds are used in negative- or positive-working radiation-sensitive mixtures. The use of such photolytic acid generators involves, however, disadvantages which drastically restrict the possible uses thereof in various fields of application. For example, many of the onium salts are toxic. Their solubility is inadequate in many solvents, which is why only a few solvents are suitable for preparing a coating solution. Furthermore, when the onium salts are used, undesired foreign atoms are sometimes introduced which can cause interference with the process, especially in microlithography. Moreover, the onium salts form Bronstedt acids, which have a very severe corrosive action, in the photolysis. These acids attack sensitive substrates, so that the use of such mixtures leads to unsatisfactory results. The halogen compounds and also the quinonediazidesulfonic acid chlorides also form hydrohalic acids which have a severely corrosive action. In addition, such compounds also have only a limited storage life on certain substrates. This was improved by inserting an interlayer between the substrate and the radiation-sensitive layer containing compounds of the type (a), but this led to an undesired increase in defects and to diminished reproducibility (see DE-A 3,621,376 equivalent to U.S. Pat. No. 4,840,867).
In more recent papers by F. M. Houlihan et al., SPIE 920, 67 (1988), it was shown by reference to positive-working systems that, in addition to the above-mentioned acid generators, nitrobenzyl tosylates, which on exposure generate sulfonic acids having a low migration tendency, can also be used in certain acid-unstable resist formulations. It can be deduced from these results that such compounds can also be used for photo-curable systems. However, the sensitivities achieved with these compounds, especially to UV radiation from 350 to 450 nm, and the thermal stability of the photoresists have proven to be inadequate.
In the U.S. Ser. No. 07/661,328, filed Feb. 27, 1991, .alpha.,.alpha.-bis-sulfonyl- or .alpha.-carbonyl-.alpha.-sulfonyldiazomethanes have been proposed as acid generators. These compounds represent an advanced state of the prior art but frequently exhibit a not entirely satisfactory thermal stability.
In spite of the intensive research activity so far carried out in this field, no radiation-sensitive mixture is at present known, by means of which a negative-working radiation-sensitive recording material can be prepared which has a high sensitivity both in the deep UV region [DUV (200 to 300 nm)] and also in the mid-UV region [MUV (300 to 350 nm)] and near-UV region [NUV (350 to 450 nm)] and high resolution, and which, even on brief irradiation, releases a sufficient quantity of an acid which does not have a corrosive action and which is sufficiently strong for cleaving compounds of type b) and, in addition, can also be developed in aqueous alkaline media.